Flexible ducting



Jan. 19, 1965 Filed April 12, 1963 D. H. DOYLY COOPER FLEXIBLE DUCTING 2 Sheets-Sheet 1 BMM ZI L BY 4% Jan. 19, 1965 0. H. DOYLY COOPER 3,166,137

FLEXIBLE DUCTING 2 Sheets-Sheet 2 Filed April 12 1963 M BY United States Patent 3,166,137 FLEXIBLE DUCTENG David Henry DOyly Cooper, Acocks Green, Birmingham, England, assignor to Dunlop Tire and Rubber Corporation, Bnfialo, N.Y., a corporation of New York Eiied Apr. 12, 3363, Eer. No. 272,573 15 Claims. (Cl. 186-7) My present invention relates to flexible ducting and more particular to flexible skirts for Hovercraft.

In one form of Hovercraft, a vehicle is suspended above ground, or above a water surface, by means of a cushion of air produced by blowing air into a plenum chamber which consists of a chamber formed between the base of the vehicle and the ground or water surface and surrounded by a skirt of flexible material. In the operational state of the Hovercraft, the vehicle is suspended pneumatically with the lower edge of the skirt clear of the ground or water surface at a height which may be as small as one inch.

When the vehicle travels over rough or stony ground or a disturbed water surface the lower edge of the skirt encounters obstacles, or waves, which deflect and lift the skirt throughout a substantial length as the vehicle passes over them, to cause undesirable loss of air pressure through the increased gap formed between the lifted portion of the skirt and the ground or water surface. Loss of air pressure in this way can cause inadvertent grounding of the Hovercraft.

In my present invention, I provide a skirt construction in which such an obstacle causes a lifting of the lower edge of the skirt only at the obstacle, causing no substantial loss of air pressure, the remaining portion of the skirt remaining in its normal position.

According to my invention a skirt, for attachment to a Hovercraft, has a series of folds about the periphery of the space enclosed by the skirt, the ridge of each fold extending from the upper to the lower edge of the skirt, and is provided with a plurality of fold-supporting members, said members being laminar in form and of flexible and resilient material more resistant to flexing than the material of the skirt, each member being attached to or incorporated in the skirt and extending parallel with the folds thereof with its plane making a substantial angle with the said peripheral direction of the portion of the skirt to which it is attached, each member being of small thickness relative to its width so that in the assembled and operational state of the skirt on the Hovercraft, when a deflecting force is applied to the lower portion thereof, the lower portion of the member will be twisted relative to the upper portion thereof. The lower portion of the skirt may deflect at the obstacle to pass over the obstacle, the fold-supporting members not affected by the deflecting force remaining in their normal positions to hold the lower margin of the skirt in its normal position.

Preferably, the skirt, considered in plan view, is of zig-zag configuration and the fold-supporting members are located with their planes extending along portions of the skirt which are disposed between adjacent ridges of the skirt.

It is preferable also that the skirt be an endless length of flexible material and each fold-supporting member be secured to one peripheral surface of the length of material. However, the skirt may comprise a plurality of hinge portions formed from flexible material, adjacent fold-supporting members being joined by said portions which are located at the ridges of the folds of the skirt.

Alternatively, the members may be attached to the ridges of the folds on either the inner side or the outer side of the skirt with respect to the Hovercraft, the members being either wholly within the skirt or on the outer side thereof, or attached to the folds of the skirt so that a part of each member lies within the plenum chamber of the Hovercraft and part outside said chamber. When the members are either wholly on the inner side or on the outer side of the skirt, it is preferable that the skirt be an endless length of flexible material.

Preferably also, in the case where'the members are attached to the ridges of the skirt, the plane of each member lies within the range from 55 to to the general peripheral direction of the neighboring portion of the skirt, but the supporting members may be disposed with their planes at right angles to said peripheral direction.

The skirt may be of rubber or rubber-like material and the fold-supporting members may also be of rubber, preferably of rubber sheet reinforced with steel or other inextensible reinforcing cords such as nylon or rayon cords. The reinforcing cords are preferably disposed in a direction which is parallel to the folds of the skirt.

The skirt may be attached at its upper edge to an annular support in the form of a relatively rigid rubber molding for attachment air-tightly to the body of the Hovercraft.

' The invention also includes a Hovercraft fitted with a skirt as defined in the preceding paragraphs.

' The invention is illustrated, by way of example, in the accompanying drawings in which: 1

FIG. 1 is an isometric View of a first embodiment of the invention, showing a portion of a Hovercraft skirt attached to a part of a Hovercraft,

FIG. 2 is a cross-sectional view of line IIII in FIG. 1 of the skirt shown in FIG. 1,

FIGS. 3 and 4 show, respectively, views similar to FIG. 2 of second and third embodiments of the invention,

FIG. 5 is a view similar to FIG. 2 showing an alternative arrangement of the third embodiment, and,

FIG. 6 is a view similar to FIG. 2 of a fourth embodiment of the invention.

In a first embodiment of the inventionas shown in FIGS. 1 and 2, a flexible skirt 1 for enclosing the plenum chamber of a Hovercraft is formed from an endless length 2 of rubber sheet, of an inch in thickness, which, as shown in FIG. 2, is of zig-zag configuration in plan View and comprises straight portions 3 extending between ridges 4. A plurality of fold-supporting members 5, which are formed from flat rectangular sheets of rubber 1 /2 inches in height, are secured, one member to each straight portion 3 of the skirt, on the inner peripheral surface 6 of the skirt, so that adjacent members 5 are disposed at an angle of 45 to one another;

The fold-supporting members 5 are reinforced by a plurality of steel filament 7 (FIG. 1) which extend longitudinally of the members and, are substantially uniformly distributed across the members, and the members extend parallel to the folds of the skirt from top to bottom of the skirt so that the steel cords are disposed in a direction of the supporting member which is vertical in the 0perational state of the Hovercraft as shown in FIG. 1.

It will be apparent that, as a fold-supporting member 5 is forced against local obstruction, the cord of steel or other material at the leading edge will be deflected and that the cords of the member will be deflected'in succession beginning with the cord first meeting the obstruction thus imparting a twist to the lower part of the member to permit the passage of the fold over the obstruction while the folds not in contact with the obstruction remain in their normal position, holding the skirt outside of the path of the obstruction in their normal position. The space between the lower edge of the skirt and the ground is accordingly not substantially increased.

The endless length 2 of rubber sheet is bonded at its upper edge to a rigid annular support 8 formed from molded rubber, the support being of L-shaped crosssection as shown in FIG. 1, having a horizontally-extending flange 9 and a vertically extending flange 10, and

being shaped to fit around the entire circumference of extending recesses 11 (part of one of which is shown in the flange 10 between the portion 12 and the flange 15.

In operation, the plenum chamber within the skirt is pressurized by the Hovercraft engine-driven fan (not shown), the resulting outward pressure on the skirt being resisted by the fold-supporting members 5." When the vehicle travels over an obstacle, the lower-edge of the skirt is deflected by the obstacle and a, component of the force exerted by the obstacle'on the skirt operates on each fold-supporting member 5, in the region deflected by 'the obstacle. This causes the member to twist and thus to present its flat side surface to the obstacle. The moment of inertia of the cross-section of .the supporting member considered along its major axis, which is'now therelevant 7 axis with the member in its twisted state, is reduced so that the fold-supporting member now offers very little resistance to deflection by the obstacle and passes over the obstacle relativelyeasily. The twisting of the members on striking an obstacle is assisted by the peripheral stretching of the skirt in the region adjacent to the area encountering the obstacle asit passes over the obstacle, on account of the turning moment applied to the members by the stretched skirt. While passing over the obstacle, the flexible nature of the fold-supporting members enables the lower portion of the skirt to conform closely to the shape of the obstacle'and to pass over it without an excessive area of the skirt being lifted, and thus avoids undue escape of air from within the plenum chamber.

In all of the alternative embodiments now to be described,.the fold-supporting members of each skirt are each of similar construction and of equal size to those described in the first embodiment and each skirt is secured to a rigid annular support similar to the support 8 of the first embodiment for air-tightly attaching the skirt to a Bovercraft. In addition, in all of the alternative embodiments to be described, deflection of thefold-supporting members in the region of'deflection of eachskirt by an obstacle, occurs in a similar manner to that described in the last preceding paragraph.

. In a second embodiment of the invention shown in FIG. 3, a skirt 16 for a Hovercraft comprises a plurality of fold-supporting members 17 and a plurality of. flexible hinge portions 18 in the form of sheets of rubber A; inchin thickness. The skirt, viewed in plan, is of zigzag configuration with the members 17 forming the straight portions of the skirt adjacent members being disposed at 45 to one another. The hinge portions, each of which is substantially U-shaped in plan view, are located one at each of the ridges 19 of the skirt, and opposite ends of each hinge portion are bonded to adjacent fold-supporting members, so that the members 17 and the hinge portions form a substantially endless length of material.

In a third embodiment shown in FIG. 4, a skirt 20 is formed from an endless length 21 of flexible rubber sheet and a plurality of fold-supporting members 22. The members 22 are secured, each by one edge, to the outer peripheral surface 23 of the length of rubber, one member being secured toeach of the inner ridges 24 of the skirt,

in relation to the center of the plenum chamber. Adja-- cent members 22 lie substantially parallel and each member lies at an angle of substantially to the general peripheral direction of the neighboring portion of the skirt. i a v In 'a modification of the third embodiment shown in FIG. 5, each member 22 is also secured by one of its longitudinally extending surfaces to a portion 29 of the length 21 of rubber which lies adjacent to the ridge 39 to which the member is secured.

In a fourth embodiment shown in FIG. 6, a skirt 25 is formed from a plurality of substantially U-shaped lengths 26 of flexible rubber sheet and a plurality of foldsupporting members 27. The fold-supporting members are located one at each of the inner ridges 28 of the skirt (with respect to the center of the plenum chamber), and each length 26 of rubber is bonded at opposite ends to adjacent supporting members 27 to form the skirt into an endless band, each member 27 projecting through the skirt and having a part on each side thereof, and a larger part of the member being located within the plenum.

chamber as shown in FIG. 6. Adjacent supporting members are parallel and each member is disposed at anangle of substantially 90 to the general peripheral direction in the neighboring portion of the skirt. 7

a In alternative arrangements of the fourth embodiment, each supporting member 27 is positioned either with an equal part on each side of the skirt, or with a largerpart locatedon the outer side'of the skirt than on the inner or plenum chamber side.

For most practical considerations, it is found that when a Hovercraft to which the skirt is fitted is travelling over rough ground and the skirt encounters obstacles on the ground, the obstacles strike the supporting members of the skirt at substantial angles to the major axes of the cross-section of the supporting members, thus ensuring that there is no likelihood of a high resistance to deflection or twisting being offered by the members. The sup porting members, therefore, offer little resistance to forward motion of the Hovercraft.

Having described my invention, I claim:

1. A skirt for a Hovercraft which comprises adjoining parallel folds of flexible resilient sheet material extending from the upper to the lower edge of said skirt and arranged in series throughout the periphery of said skirt to form alternate, substantially vertical, inner and outer ridges, fold supporting members, at least one for each pair of inner and outer ridges of said series, each of said fold supporting members comprising a stripof flexible, resilient, material extending from the upper edge to the lower edge of said skirt and each being secured in fixed position in said skirt, and means at the upper edge margin of said skirt to hold said folds and said fold-supporting members in fixed position with the plane of said strip of each foldsupp'orting member at a substantial angle with the peripheral direction of the portion of the skirt to which it is attached, each said strip having suflicient stiflness to hold said skirt in position under normal operating conditions and of suflicient resilience to twist and bend under force applied at its lower end.

2'. A skirt according to claim 1 wherein, considered in plan View, the skirt is of zig-zag configuration and the fold-supporting members are located in planes which extend along portions of the skirt which are disposed between adjacent ridges of the skirt. 7 V 3. A skirt according to claim 2 wherein the skirt comprises an endless lengthof flexible material and each fold-supporting member is secured to one peripheral surface of the length of material.

4. A skirt according to claim 2 wherein the skirt comprises a plurality of hinge. portions formed of flexible material, said hinge portions being disposed one at each of the ridges of the skirt and joining adjacent fold-supporting members to form the skirt. 7

5. A skirt according to claim 1 wherein the fold-sup- 7. A skirt according to claim 6 wherein the fold-supporting members are alsosecured to portions of the skirt which lie adjacent to the ridges to which the members are secured.

8. A skirt according to claim 5 wherein the skirt corn-v the plane of each fold-supporting member lies at an angle of between 55 and 90 to the general peripheral direction of the neighboring portion of the skirt.

- 10. A skirt according to claim 1 whereinthe skirt and the fold-supporting members are formed of rubber.

11. A skirt according to claim lO wherein the foldforcing cords are disposed in a direction which'is parallel supporting membersare reinforced with substantially in- V I extensible cords. v I 1 i 12. A skirt according toclaim 11 wherein the rein- 1 forcing cords in the fold-supporting members comprise steel filaments.

'13.-A skirt accordi ng' to clairnl ll wherein the rein-"' ARNGLD Examiner.-

to-the folds of the skirt.

. 14. A sMrt according to claim 1 wherein the skirt is attached at its upper edge to a rigid annular support for attachment air-tightly to the body of a Hovercraft.

15. A Hovercraft fitted with a skirt aecordingto.

claim 1.

References Cited by the Examiner UNITED STATES PATENTS 3,027,860" 4/62 Priest 1s0 7 3,055,446 9/ 62 ,Vaughen 180'-7 3,082,836 3/63 'Billmana 1s0 7 3,120,832 2/64 'Buisson 11s 1- A V'FOREIGN PATENTS. 1,238,499 7/60 France.

OTHER REFERENCES 4,

the Record.

Me cl1. Eng, June 1962, pages 66 and 67, Briefin A. LEVY, Primary Examiner. 

1. A SKIRT FOR A HOVERCRAFT WHICH COMPRISES ADJOINING PARALLEL FOLDS OF FLEXIBLE RESILIENT SHEET MATERIAL EXTENDING FROM THE UPPER TO THE LOWER EDGE OF SAID SKIRT AND ARRANGED IN SERIES THROUGHOUT THE PERIPHERAY OF SAID SKIRT TO FORM ALTERNATE, SUBSTANTIALLY VERTICAL, INNER AND OUTER RIDGES, FOLD SUPPORTING MEMBERS, AT LEAST ONE FOR EACH PAIR OF INNER AND OUTER RIDGES OF SAID SERIES, EACH OF SAID FOLD SUPPORTING MEMBERS COMPRISING A STRIP OF FLEXIBLE, RESILIENT, MATERIAL EXTENDING FROM THE UPPER EDGE TO THE LOWER EDGE OF SAID SKIRT AND EACH BEING SECURED IN FIXED POSITION IN SAID SKIRT, AND MEANS AT THE UPPER EDGE MARGIN OF SAID SKIRT TO HOLD SAID FOLDS AND SAID FOLD-SUPPORTING MEMBERS IN FIXED POSITION WITH THE PLANE OF SAID STRIP OF EACH FOLD SUPPORTING MEMBER AT A SUBSTANTIAL ANGLE WITH THE PERIPHERAL DIRECTION OF THE PORTION OF THE SKIRT TO WHICH IT IS ATTACHED, EACH SAID STRIP HAVING SUFFICIENT STIFFNESS TO HOLD SAID SKIRT IN POSITION UNDER NORMAL OPERATING CONDITIONS AND OF SUFFICIENT RESILIENCE TO TWIST AND BEND UNDER FORCE APPLIED AT ITS LOWER END. 